The ephrin receptors (Eph) super family shares 65-90% sequence homology in the kinase domain and 30-70% in the extracellular domain. At least 15 members of the Eph super family have been identified, from vertebrates, Drosophila and C. elegans, and it is the largest sub-family of receptor tyrosine kinases (RTKs), which itself is divided into two sub-groups. The first group is based on ligand-binding affinity whereas the second group is based on the structure of the extracellular domain.
The ephrin ligands are referred to hereafter as “Ephrin” and bind to the ephrin receptor referred to hereafter as “Eph”.
The EphA (A1-A9) generally binds Ephrin A members that are linked to the plasma membrane through a glycosylphosphatidylinositol anchor, whereas the EphB (B1-B6) receptors generally bind Ephrin B members that transverse the cell membrane. Structurally, Eph receptors comprise an extracellular globular domain responsible for ligand binding, a cysteine-rich region, two fibronectin type III repeats, a region spanning the cell membrane, and a tyrosine kinase domain. (Tandon et al., 2011)
Within the Eph family, receptor-ligand binding occurs without discrimination between each subclass of the family, for example EphA4 binds Ephrin B with high affinity (Murai and Pasquale, 2003). Moreover, the Ephrins, which are membrane bound proteins, mediate bi-directional signals between adjacent cells. Interactions between Eph and Ephrin on adjacent cells promote the clustering of these molecules, which leads to the initiation of the signal, involving tyrosine phosphorylation mediated by Eph RTKs, and in turn results in the activation of various intracellular signaling pathways.
The role of Ephrin-Eph signaling is known in CNS, controlling development of neuronal networks, axon guidance and nervous system repair (Pasquale, 2008). Moreover, the cell-cell contact-dependent functioning of Eph and Ephrin is tightly regulated during normal embryonic development and maintenance of homeostasis. However during oncogenesis due to loss of cell contacts, the normal EphA2-Ephrin A1 signaling is disrupted, leading to overexpression of EphA2 and oncogenic signal transduction. This deregulated signaling leads to cytoskeleton modulation, cell adhesion, migration, metastasis, proliferation and angiogenesis, all being hallmarks of oncogenesis (Tandon et al., 2011; Xi et al., 2012).
EphA2 is overexpressed in several cancers including breast, ovarian, prostatic, pancreatic, lung, melanoma and colorectal cancer, as well as glioblastoma multiformes. In a large proportion of cases, EphA2 overexpression is correlated to advanced-stage disease or metastatic stage disease.
In breast cancer, EphA2 protein levels are increased in aggressive breast cancer cell lines versus non-transformed mammary epithelial cells, whereas EphA2 overexpression in breast cancer cells is negatively correlated with epidermal growth factor receptor (ER) expression. Interestingly, constitutive expression of EphA2 confers intrinsic resistance to trastuzumab in human epidermal growth factor receptor-2 (HER2) overexpressing cells, and therefore decreases the therapeutic effect of trastuzumab. These findings are further supported by clinical observations correlating high EphA2 expression levels with reduced overall and recurrence-free survival rates (Brantley-Sieders et al., 2011) on the one hand, and correlating EphA2 mRNA levels increase with overall survival of HER2-positive breast cancer patients, on the other hand (Zhuang et al., 2010). Consequently, inhibition of EphA2 expression may represent a promising avenue to reverse tratuzumab resistance.
In addition, it was also reported that EphA2 antisense oligonucleotides reduced the growth of the triple negative breast cancer cell lines MDA-MB-231 (Carles-Kinch et al., 2002).
Beyond EphA2, which plays a key role in breast cancer, several other Eph have been reported for their tumor promoter role and/or their expression has been correlated to poor prognosis like EphA4, EphB4, and EphB6.
In addition to the roles on neuronal and angiogenic patterning, EphB family members have a role in inflammation (Ivanov et al., 2005; Kitamura et al., 2008; Zamora et al., 2006), bone metabolism (Zhao et al., 2006) and in osteoarthritic bone remodeling. (Kwan Tat et al., 2008)
Finally, EphA and Ephrin A have been ascribed a role in the regulation of glucose, more specifically in the pancreatic beta cells. EphA were reported to negatively regulate insulin production, while reverse signaling through the Ephrin ligands would upregulate insuline production. Increased glucose levels trigger dephosphorylation and therefore inactivation of the receptor kinase and cause ephrin reverse signaling. Thus the insulin steady state level is dependent on the interaction between the ligand and the receptor, and by the active state of the receptor (Konstantinova et al., 2007).
Although currently a number of treatments for type 2 diabetes exist, they are accompanied by more or less serious side effects (Bolen et al., 2007). Therefore, there remains a need for an effective treatment for diabetes.
There is therefore a need to identify further compounds which may be effective in the treatment and/or prophylaxis of these diseases.
US 2010/0113415 (Rajapakse et al., 2010) discloses 1H-pyrazolo[3,4-b]pyridin-3-yl compounds, all of which must have an amino group in position 3.
The present invention provides compounds, methods for their manufacture and pharmaceutical compositions comprising a compound of the invention together with a suitable pharmaceutical carrier, which compounds and compositions may be used in the treatment and/or prophylaxis of these diseases. The present invention also provides for the use of a compound of the invention in the preparation of a medicine for the treatment of for the prophylaxis and/or treatment of diseases including inflammatory conditions, type 2 diabetes, neurological and/or neurodegenerative diseases, autoimmune diseases, proliferative diseases (in particular metastatic diseases, and/or cancer), abnormal angiogenesis associated diseases, degradation of cartilage, and/or disruption of cartilage homeostasis.